1. Special Senses

2. The Senses 1. General senses of touch 2. Special senses Temperature
Pressure
Pain
2. Special senses
Smell
Taste
Sight
Hearing
Equilibrium

3. Eyes and Vision: The major parts of the Eye (external) Eyelids
Close to protect the eyes.
Eyelashes
Additional protection for the eye.
Conjunctiva
Covers the “white” part of the eye and the inner eyelid. Creates mucus.
Sclera
The white part of the eye.
Iris
Contractile tissue that allows light to enter the eye.

4. Lacrimization: (aka crying)
The entire lacrimal system involves 3 structures.
Lacrimal ducts
Superior & Inferior
Lacrimal Glands
Carry excess tears out of the orbit of the eye
Continuously release a dilute salt solution onto the anterior surface of the eye through small ducts in the eyelid
Lacrimal sac
Collects the excess tears and moves it to the nasal cavity

5. Muscles of the Eye Muscles attach to the outer surface of the eye
Rectus muscles attach anterior to posterior
Muscles attach to the outer surface of the eye
Produce eye movements
Oblique muscles attach laterally and medially

6. Structure of the Eye The wall is composed of three tunics
Sclera&Cornea fibrous outside layer
Choroid – middle layer
Sensory tunic – (retina) inside layer
Figure 8.3a

7. The Fibrous Tunic Sclera Cornea White connective tissue layer
Seen anteriorly as the “white of the eye”
Cornea
Transparent, central anterior portion
Allows for light to pass through
Repairs itself easily
The only human tissue that can be transplanted without fear of rejection

8. Choroid Layer Blood-rich nutritive tunic
Pigment prevents light from scattering
Modified interiorly into two structures
Cilliary body – smooth muscle
Iris
Pigmented layer that gives eye color
Pupil – rounded opening in the iris

9. Sensory Tunic (Retina)
Contains receptor cells (photoreceptors)
Rods
Cones
Signals pass from photoreceptors and leave the retina toward the brain through the optic nerve

10. Neurons of the Retina

11. Neurons of the Retina and Vision
Rods
Most are found towards the edges of the retina
Allow dim light vision and peripheral vision
Perception is all in gray tones

12. Neurons of the Retina and Vision
Cones – 3 types detect different colors
Densest in the center of the retina
Fovea centralis – area of the retina with only cones
Lack of one type = color blindness
No photoreceptor cells are at the optic disk, or blind spot

13. Lens Biconvex crystal-like structure
Held in place by a suspensory ligament attached to the ciliary body

14. Internal Eye Chamber Fluids
Aqueous humor in Anterior Segment
Watery fluid found in chamber between the lens and cornea
Similar to blood plasma
Helps maintain intraocular pressure
Provides nutrients for the lens and cornea
Reabsorbed into venous blood
Blocked drainage = glaucoma

15. Internal Eye Chamber Fluids
Vitreous humor in Posterior Segment
Gel-like substance behind the lens
Keeps the eye from collapsing
Lasts a lifetime and is not replaced

16. Color Blindness (AKA Daltonism) is a dysfunction of the cones of some type. Look at the following plates and write down what you see.
Plate 1
Plate 2

17. Plate 3
Plate 4
Plate 5

18. Plate 6
Plate 7
Plate 8

19. Plate 9
Plate10
Plate 11

20. Results of Colorblindness test
Plate 1 – Everyone can see the number 12
Plate 2 – Normal – number 8
Red/Green – number 3
Total – nothing
Plate 3 – Normal – number 29
Red/Green – number 70
Plate 4 – Normal – number 5
Red/Green – number 2
Plate 5 – Normal – number 3
red/Green – number 5
Plate 6 – Normal – nothing but wavy lines
Red/Green – number 5

21. Plate 7 – Normal – nothing but wavy lines
Red/Green – number 45
Plate 8 – Normal – should see a red and purple line
Red – a purple line
Green – red line
Plate 9 – Normal – a green wiggly line
Any color blindness – no line
Plate 10 – Normal – green wiggly line
Red – a blue-green and a red line
total – no lines
Plate 11 – Everyone should see a line
Remember: No test is totally accurate. These are only indicators. Don’t go off telling everyone that you are “normal” or “colorblind” until you have seen a professional.

22. Close your left eye and stare at the cross
Close your left eye and stare at the cross . You may need to move away or toward the screen. At some distance, the dot will dissolve.

23. So how many feet do elephants have?
Optical illusions:
Because your eyes and brain “matrix” pictures to create a solid image in your mind, these images may “fool” you into believing they are something they are not!
So how many feet do elephants have?

24. Which is raised, the up or the sideways?

25. Do these images move on their own?

26. Lens Accommodation
Light must be focused to a point on the retina for optimal vision
The eye is set for distance vision (over 20 ft away)
The lens must change shape to focus for closer objects

27. Eye Focus Terms: Correct Focus = Emmetropia
The lens has the ability to focus images from any distance upon the retina to receive a clear image.

28. Nearsightedness = myopia
Focus of light in front of retina
Eyeball too long or
lens too strong
Distant objects are
blurry

29. Farsightedness = hyperopia
Focus of light beyond the retina
Short eyeball or lazy lens
Near objects are blurry.

30. Astigmatism
Unequal curvatures in cornea & lens

31. What happens if the cones or rods are not functioning correctly?
The term is “Chromatic Deficiency”
We would call it color blindness
There are several types:
Monochromacy – total colorblindness
Dichromacy – one of the three color cones is not functioning.
Anomalous Trichromacy – where one of the three colors is altered so that there is not true color vision

32. Red/Green colorblindness
Rod Monochromacy (the most rare) – where all cones are non-functioning.
The most common are types of Dichromacy
Red/Green colorblindness
A sex linked trait (more common in males) carried on the X chromosome of the 23rd pair. Inability to distinguish between the red and green spectrum.
What do you see?

33. The Ear Houses two senses Receptors are mechanoreceptors Hearing
Equilibrium (balance)
Receptors are mechanoreceptors

34. Anatomy of the Ear The ear is divided into three areas
Outer (external) ear
Middle ear
Inner ear

35. The External Ear Involved in hearing only
Structures of the external ear
Pinna (auricle)
External auditory canal

36. The External Auditory Canal
Narrow chamber in the temporal bone
Lined with skin
Ceruminous (wax) glands are present
Ends at the tympanic membrane

37. The Middle Ear or Tympanic Cavity
Air-filled cavity within the temporal bone
Only involved in the sense of hearing
Two tubes are associated with the inner ear
The opening from the auditory canal is covered by the tympanic membrane
The auditory tube (eustachian tube) connecting the middle ear with the throat
Allows for equalizing pressure during yawning or swallowing
This tube is otherwise collapsed

38. Bones of the Tympanic Cavity
Three bones span the cavity
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)

39. Sound travels in and makes the tympanic membrane *
vibrate
The hammer
moves the anvil
which moves the stirrup
This vibrates the oval window*

40. Bones of the Tympanic Cavity
Vibrations from eardrum move the malleus
These bones transfer sound to the inner ear

41. Inner Ear or Bony Labyrinth
Includes sense organs for hearing and balance
Filled with peri-lymph

42. Inner Ear or Bony Labrynth
A maze of bony chambers within the temporal bone
Cochlea
Vestibule
Semicircular canals

43. Organs of Hearing Organ of Corti Located within the cochlea
Receptors = hair cells on the basilar membrane
Gel-like tectorial membrane is capable of bending hair cells
Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe
Slide 8.27a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

44. Organs of Hearing

45. Mechanisms of Hearing
Vibrations from sound waves move tectorial membrane
Hair cells are bent by the membrane
An action potential starts in the cochlear nerve
Continued stimulation can lead to adaptation

46. Mechanisms of Hearing

47. Organs of Equilibrium Receptor cells are in two structures Vestibule
Semicircular canals

48. Organs of Equilibrium Equilibrium has two functional parts
Static equilibrium – sense of gravity at rest
Dynamic equilibrium – angular and rotary head movements

49. Static Equilibrium - Rest
Maculae – receptors in the vestibule
Report on the position of the head
Send information via the vestibular nerve
Anatomy of the maculae
Hair cells are embedded in the otolithic membrane
Otoliths (tiny stones) float in a gel around the hair cells
Movements cause otoliths to bend the hair cells

50. Function of Maculae

51. Dynamic Equilibrium - Movement
Crista ampullaris – receptors in the semicircular canals
Tuft of hair cells
Cupula (gelatinous cap) covers the hair cells

52. Dynamic Equilibrium Action of angular head movements
The cupula stimulates the hair cells
An impulse is sent via the vestibular nerve to the cerebellum

53. Chemical Senses – Taste and Smell
Both senses use chemoreceptors
Stimulated by chemicals in solution
Taste has four types of receptors
Smell can differentiate a large range of chemicals
Both senses complement each other and respond to many of the same stimuli

54. Olfaction – The Sense of Smell
Olfactory receptors are in the roof of the nasal cavity
Neurons with long cilia
Chemicals must be dissolved in mucus for detection
Impulses are transmitted via the olfactory nerve
Interpretation of smells is made in the cortex

55. Olfactory Epithelium

56. The Sense of Taste Taste buds house the receptor organs
Location of taste buds
Most are on the tongue
Soft palate
Cheeks

57. The Tongue and Taste
The tongue is covered with projections called papillae
Filiform papillae – sharp with no taste buds
Fungifiorm papillae – rounded with taste buds
Circumvallate papillae – large papillae with taste buds
Taste buds are found on the sides of papillae

58. Structure of Taste Buds
Gustatory cells are the receptors
Have gustatory hairs (long microvilli)
Hairs are stimulated by chemicals dissolved in saliva
Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas
Facial nerve
Glossopharyngeal nerve
Vagus nerve

59. Anatomy of Taste Buds
Figure 8.18

60. Taste Sensations Sweet receptors Sour receptors Bitter receptors
Sugars
Saccharine
Some amino acids
Sour receptors
Acids
Bitter receptors
Alkaloids
Salty receptors
Metal ions
Slide 8.41
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

61. Developmental Aspects of the Special Senses
Formed early in embryonic development
Eyes are outgrowths of the brain
All special senses are functional at birth
Slide 8.42
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

62. Review for test: Define: Answer The following:
1. Conjunctiva 2. Sclera 3. Lacrimization
4. First tunic 5. Second Tunic 6. Third Tunic
sclera & Cornea Chorid layer Sensory Tunic
7. Rods 8. Cones 9. Fovea Centralis
10. Lens 11. Aqueous Humor 12. Vitreous Humor
13. Emmetropia 14. Myopia 15. Hyperopia
16. Pinna 17. Malleus 18. Incus
19. Stapes 20. Tympanic membrane 21. Oval window
22. Organ of Corti 23. Vestibule 24. Semicircular Canal
25. Endolymph 26. Crista Ampullaris 27. Cupula
28. Fungiform papilla 29. Circumvallate papilla 30. Olfactory
31. Gustatory
Answer The following:
What are the structures of the middle and inner ear, and how do they help us hear?
Explain fully the term – Chromatic deficiency
How does balance happen with the human ear?